NOTE: I now use Phenoseal to seal the wood inside the unit.
HI Bill,
While I would never call myself an expert at anything, I have
spent many days perfecting the rebuilding of the Simplex block
valve/pneumatic to the point where they work every single time.
The vast majority of the units that failed early on did so
because of leakage through the wood or through the mounting
screw holes. Depending on the technique that you used to take
the blocks apart, there could be microscopic cracks between
the upper and lower valve chamber.
To eliminate the possibility of such leakage, I reseal every
square millimeter on the inside of the unit. In the pouch well
and the lower half of the valve chamber, I use shellac, two
thick coats. I also seal the hole leading to the pouch well
and the vacuum channel with shellac. And, after the blocks are
back together, I seal the area on the block that's inside
the pneumatic and the vacuum channel leading from the exhaust
side of the valve to the inside of the pneumatic, including
the slit section. To seal the area in the upper half of valve
chamber, around the metal valve seat, I use Phenoseal. But I
don't just paint it on. After I apply a thin coat, I close
off seat with my finger and suck gently on the supply channel.
This sucks the Phenoseal into the wood. After that's dry, I
apply another thin coat and then blow gently into the vacuum
channel. If there is any wood leakage, the Phenoseal will
bubble up, identifying the leaking area. In each case where
leakage was detected, the air was leaking through the chamber
walls, and not around the valve seat (since it is sealed on
the underside with shellac). Quite honestly, I've never been
able to pin point exactly where the air is coming in, but my
belief is that it is coming in through the open mounting
screw holes.
(I made a 3-perspective drawing of the block to see how
close the screw holes are to the valve chambers and pouch
wells and it's measured in millimeters. So such leakage is
extremely plausible. You might also find that if that is indeed
the problem, it will magically disappear when the blocks are
installed into the piano, since those holes are totally
closed off from outside air by the screw.)
Now I'll back up a little. Unlike most rebuilders, I do not
seal the pouches. And it is for that reason that I am
responding to your posting privately. We could get into a very
long draw out discussion about the benefits and drawbacks of
sealing the pouches, but common sense tells me that if you
add anything to the pouch leather, the flexibility of the leather
decreases. The question I asked myself from square one was:
if sealing the pouches is so important, why didn't the
manufacturer seal them? Since they felt no need to do it, I
don't either.
Moving on. When I put the block back together, the two halves
are dry fit to see if there is any warpage. And if there is,
the warped half or halves are lightly sanded. I also use a
fairly substantial amount of hot hide glue when glueing the
pieces back together, especially around the air channel
leading into the pneumatic. I found that since the edge of
the pouch is dangerously close to that opening, air can
seep underneath (or through the edge) of the pouch, allowing
atmospheric air into the pouch well. This causes the pouch
to rise when being tested, like the note is turned 'on'. When
the pouch is also sealed (on top), making it more air tight
than ever intended, the whole situation becomes even more
critical, and even the slightest leakage through the edge
of the pouch will trigger the note.
One thing I know for absolute positive is that a pouch will
not move if there is an equal amount of vacuum on both sides
of the leather. And only two things can change that state.
One, the entrance of atmospheric air (or reduced vacuum)
on the underside of the pouch. Two, the entrance of a higher
vacuum level above the pouch. Since #2 is basically
impossible, that leaves #1. The question then becomes: where
is the air leaking 'in'? Eliminating every possible place
(even through the wood) where air can leak 'in' eliminates
the possibility of a problem.
Musically,
John A. Tuttle
===========================================================
One of the real headaches about the Simplex unit is
the proximity of the pneumatic air channel and the
pouch chamber (both above and below the pouch). They
are quite close to each other and even the slightest
leakage between the two will render a unit useless.
I noticed when opening the blocks that Simplex was not
adverse to using copious amounts of hide glue. The
evidence is everywhere. They knew how critical it was
to have complete separation between the two spaces
and that each space had to be air tight. Glue filled
any and all of the voids and regularly was seen all
around the edges on the pouch, infringing on the
operating area by as much as 1/8" nearly all the way
around.
The reality that Simplex was in no way concerned about
the 'over-flowing' glue onto the operating portions of
the pouch, got me to wondering about the often overstated
importance of pouch placement. It's often been said that
a pneumatic-operated pouch-setting tool must be used to
reduce the possibility of dragging the glue into the
operating portion of the pouch well. While this is reasonable
in instances where the pouch is 'free standing' on a pouch
board, it is a totally unnecessary concern when applying
the pouches in the Simplex block.
Simplex obviously designed the pouch to be big enough in
total size that losing 1/8" all the way around was of no
significance at all. In fact, when you examine the physics
of the matter, a smaller pouch will react faster than a
larger pouch (all other factors being the same). So one
has to consider that Simplex actually planned on using
lots of glue to put the blocks together, knowing that, in
a sense, 'more was better'.
I noticed during the rebuilding of an entire set; the
units I had problems with were the ones where I had been
skimpy with the hide glue, when putting the blocks back
together. Also, the consistency of the glue was definitely
a factor. I constantly added small amounts of water to keep
the glue at just the right thickness.

This page was last revised
July 1, 2017 by John A. Tuttle, who Assumes No
LiabilityFor The Accuracy or Validity of the Statements and/or Opinions
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